VIATRA/Query/UserDocumentation/API/RunOnce

Overview

This page describes how EMF-IncQuery can be used to carry out one-time query evaluation which is useful in the following cases:

• You want less (steady-state) memory consumption instead of incremental evaluation.
• You have derived features that are not well-behaving, but you want to include them in queries.
• You like the query language of EMF-IncQuery, but you don't need incremental evaluation and the batch performance is better than the sum of model modification overheads between query usages.

These scenarios are now supported by a "run-once" query engine that will perform the evaluation on a given query and return the match set then dispose of the Rete network and base index to free up memory.

Example

The up-to-date sample source code to this page is found in Git here: http://git.eclipse.org/c/incquery/org.eclipse.incquery.examples.git/tree/minilibrary Most notably,

• the patterns are found in eiqlibrary.eiq
• and the API usage samples are found in RunOnceTest.java

Usage

The API of the run-once query engine is very simple, just instantiate the engine with the constructor using the proper scope (EObject, Resource or ResourceSet) and call the getAllMatches with a query specfication:

RunOnceQueryEngine engine = new RunOnceQueryEngine(notifier);
// using generated query specification
Collection<SumOfPagesInLibraryMatch> allMatches = engine.getAllMatches(SumOfPagesInLibraryMatcher.querySpecification());
// using generic query specification
GenericQuerySpecification specification = new GenericQuerySpecification(BooksWithMultipleAuthorsMatcher.querySpecification().getPattern());
Collection<GenericPatternMatch> matches = engine.getAllMatches(specification);